public PowerRepository(string connString) : this()
 {
     DbContext = new PowerDbContext(connString);
 }
 public PowerRepository(PowerDbContext dbContext)
 {
     DbContext = dbContext;
 }
 /// <summary>
 /// 创建一个新的数据仓库泛型基类对象
 /// </summary>
 public PowerRepository()
 {
     DbContext = new PowerDbContext();
 }